Use of fluoboric acid as a means of removing core sands from castings



: g fts Patented Mar. 28, 1950 USE OF FLUOBORIC ACID AS A MEANS OF REMOVING CORE SANDS FROM CAST- INGS Harry L. Moir, Glencoe, Ill., assignor to The Pure Oil Company, Chicago, Ill., a corporation of Ohio No Drawing. Application September 28, 1944, Serial No. 556,290

This invention relates to a method for removing sand from metal castings made with core sand patterns.

In the casting of metal forms, particularly cast iron forms of intricate design using core sand patterns, it is sometimes extremely difiicult to completely remove the sand from the casting. I have discovered that residual sand which adheres to the casting can be removed by subjecting the casting to treatment with fluoboric acid containing an inhibitor to inhibit the action of the acid on the metal. Fluoboric acid dissolves silica thereby removing it from the metal casting and leaving the casting with a clean surface.

" It has already been proposed to remove sand without agitation, agitation is preferred because it speeds up the reaction. The sand grains are dissolved by the acid, and the solution so formed tends to settle toward the bottom of the treating vessel, thereby exposing the castings to fresh fluoboric acid.

Fluoboric acid can be prepared by simply mixing proper quantities of hydrofluoric and boric acids together. It may also be prepared by adding suitable fluoride and borate salts to mineral acid solution so that the fluorides and borates are converted to hydrofluoric and boric acids, respectively, which, in turn, react to form the fluoboric acid. Suitable fluorides and borates which may be used are the sodium, potassium and ammonium salts, as well as other metal fluorides and borates which are readily soluble in the mineral acid used to dissolve them. Another method for making fluoboric acid is to pass boron trifluoride gas into aqueous hydrofluoric acid.

In preparing hydrofluoric acid it is preferred to use reactants in such proportion that the molal ratio of fluorine to boron in the composition is not less than 4 to 1, in order to form the acid HBFi. In general, a small excess of hydrofluoric acid should be present in the fluoboric acid solution. The amount of excess hydrofluoric acid over and above the fluoboric acid should not exceed 50% by weight of the fluoboric acid present,

11 Claims. (Cl. 1343) and preferably not over approximately 10% by weight. Suitable corrosion inhibitors such as arsenicacid, arsenic'trioxide or soluble arsenates affd' arsenites, such as the alkali metal salts, cyanides, aniline, phenyl-hydrazine, pyridine, quinoline, acridine and mercaptans may be added in small amounts ranging from approximately 0.5% to approximately 5% by weight of the solution.

A suitable acidagent for cleaning iron casting '5 may be prepared by adding 61.8 grams of solid boric acid to 166.8 grams of 48% aqueous hydrofluoric acid. This produces a reagent containing 38.4% by weight of fluoboric acid. To the resulting acid solution is added approximately 2% of arsenic acid. A solution prepared as just described will efiectively clean adhering sand particles from iron castings within a relatively short time, depending upon the amount of sand adhering to the casting. Care shouldbe exercised not to make the solution so dilute as to render it in'-' effective or only slightly effective. Solutions having a fluoboric acid content of 20% or greater may be used.

After the sand has been completely removed from the casting itis removed from the acid bath and placed in a bath of hot water to remove the adhering acid from the casting.

The acid bath must be renewed from time to time as the density thereof becomes too great, or the acid content thereof becomes too low for effective use.

It will be seen, therefore, that I have discovered an effective method for cleaning metal castings in order to remove adhering mineral particles from portions thereof, which can be cleaned only with great difliculty by mechanical or other means.

It is claimed:

' 1. The method of removing sand from metal castings cast with sand core patterns comprising contacting said casting with fluoboric acid.

2. The method of removing siliceous material from iron surfaces comprises bringing said material into contact with fluoboric acid.

3. The method of removing siliceous material from iron surfaces comprising contacting said material with fluoboric acid containing a substance capable of inhibiting the action of the fluoboric acid on the iron.

4. The method of removing sand from iron castings comprising immersing said castings in a bath of boric and hydrofluoric acids in which hydrofluoric acid is present in excess of the amount necessary to react with boric acid to form fluoboric acid.

Bearer 5. Method in accordance with claim 4 in which the excess hydrofluoric acid is not more than approximately 10% of the fluoboric acid.

6. Method in accordance with claim 1 in which the fiuoboric acid contains a small amount of hydrofluoric acid and a material capable of inhibiting the action of the acid on the metal castings.

7. The method of removing .siliceousm'aterial...

from metal surfaces comprising immersing said surfaces in an aqueous bath containing at least 20% by weight of fluoboric acid, an amount of hydrofluoric acid less than half the amount 'of fluoboric acid and a small amount of a substance capable of inhibiting the action of the acids on the metal.

8. Method in accordance with claim '7 in which;

the metal surfaces are iron and the bath contains approximately 38.4% by weight of fluoboric acid.

9. The method of removing sand from metal castings which comprises contacting said castings with fluoboric acid of suficient concentration to attack the sand in the presence of a substance capable of inhibiting the acid from attacking themetal.

10. Method in accordance with claim 9 in which the fluoboric acid contains a small amount of hydrofluoric acid.

11. The method of removing siliceous material from metal surfaces comprising immersing said surfaces in an aqueous bath containing at least 20% by weight of fiuoboric acid and 'a small amount of hydrofluoric acid.

HARRY L. MOIR.

REFERENCES CITED The following .references are of record in the file of this patent:

UNITED STATES PATENTS 

7. THE METHOD OF REMOVING SILICEOUS MATERIAL FROM METAL SURFACES COMPRISING IMMERSING SAID SURFACES IN AN AQUEOUS BATH CONTAINING AT LEAST 20% BY WEIGHT OF FLUBORIC ACID, AN AMOUNT OF HYDROFLUORIC ACID LESS THAN HALF THE AMOUNT OF FLUOBORIC ACID AND A SMALL AMOUNT OF A SUBSTANCE CAPABLE OF INHIBITING THE ACTION OF THE ACIDS ON THE METAL. 